Among polymeric materials, epoxy resin material has long been in use in coating and semiconductor packaging, because it is resistant to solvents, easy to process, and suitable for use with an appropriate curing agent. Rapid development of electronic products is accompanied by increasingly strict restriction of application of epoxy resin because of its disadvantages: high flammability and high dielectric constant. Highly ductile and thermally stable, aromatic polyethers are suitable for use as epoxy resin tougheners. commercially-available aromatic polyethers used as tougheners are mostly provided in the form of oligomers such that a terminal reacting group thereof serves to cure epoxy resins. However, owing to a scarcity of their reacting groups, aromatic polyethers cannot work without any curing agent. Hence, their modifying function with respect to epoxy resins still has room for improvement.
To this end, the industrial sector developed a polyether with an active group, which is not only capable of curing and toughening, but also effective in improving the characteristics and applications of epoxy resins. In 2013, Lin and others (Polymer, 2013, 54 (6), 1612-1620) disclosed producing, by one-pot reaction, polyetheretherketone (PEEK) and polysulfones which have repeating units. The repeating units each have an active group and a flame-retarding structure. The active group of the repeating unit contributes to flexible applications of polymers. The hydroxyl group of the structure serves as an epoxy resin curing agent. The phosphorus-based structure renders a cured product flame-retarding and cures epoxy resins to thereby achieve a satisfactory glass transition temperature Tg. However, the hydroxyl group produces high-polarity secondary alcohol while curing epoxy resins, and thus remains unsatisfactory in terms of the dielectric constant.
In 2014, U.S. Pat. No. 8,791,214 B2 disclosed esterification of phenolic compounds, namely phenol novolac (PN) and dicyclopentadiene phenol novolac (DCPDPN), by mono-group or bi-group acyl chloride before the resultant ester cures epoxy resin HP7200, wherein ring-opening reactions of the epoxy resin is accompanied by transesterification which takes place in the presence of an active ester. After the epoxy resin has been cured, production of high-polarity secondary alcohol is impossible and thus conducive to a reduction in the dielectric constant. However, after reacting with the epoxy resin, the active ester substitutes for the hydroxyl group of the ring-opened epoxy resin and thus weakens intermolecular hydrogen bonds, thereby lowering the Tg of the cured product.
In addition to modifying an active hydroxyl group, dicyclopentdiene (DCPD) is easy to process because it is a high-rigidity aliphatic dicyclic compound and a promising green material. In 2004, Huang and others (Journal of Applied Polymer Science, 2005, 96, 2079-2089) disclosed introducing DCPD into cyanate ester and comparing it with commercially-available bisphenol A cyanate ester, and the findings showed a marked decrease in its dielectric constant. In 2006, Huang and others (Polymer International, 2006, 55, 1341-1349) disclosed introducing DCPD into bismaleimide to prove that its cured product has satisfactory dielectric characteristics.
The above citation documents show that introduction of a polyether into DCPD is conducive to improvement of electrical characteristics and enhancement of processability. Hence, the industrial sector currently needs a method of producing a DCPD-derived polyether and thereby producing a polyether material which not only features low-k characteristics, high thermal properties, and high mechanical strength, but is also non-flammable and curable, so that the polyether material can be applied to optoelectronics.